Moveable seat for crystal in an oscillating crystal transducer systems

Abstract

A transducer capable of measuring force or fluid pressure comprises one or more plate-like crystals; electrical means for exciting each crystal into resonance; a base upon which sits a first seating which supports the lower edge of said one crystal; a second seating disposed at the upper edge of the crystal so as to secure the crystal in a position perpendicular to said base; each seating comprising cylindrical or semi-cylindrical surfaces the cylindrical faces of which, are arranged to bear on the crystal edge so as to produce, in response to said force, a change of the resonant frequency of that crystal with respect to the other crystal or crystals.

I claim: 
     
       1. A force transducer comprising: a plate-shaped crystal having a peripheral edge with a curved portion, and   at least one seating member which engages the curved portion of the peripheral edge of the crystal and has a convex surface curved in the direction opposite to that of the peripheral edge curved portion providing a contact region which is more limited in length along the length of the peripheral edge than the contact region provided by a flat seating member.   
     
     
       2. A force transducer according to claim 1 including a thin layer of a material which is physically softer than the crystal and the seating member mounted on the surface of the seating member. 
     
     
       3. A force transducer according to claim 2 wherein the thin layer of material is deformed at the contact region to conform to the shape of the peripheral edge curved portion. 
     
     
       4. A force transducer according to claim 1 including spring means urging the seating member against the curved portion of the peripheral edge of the crystal. 
     
     
       5. A force transducer according to claim 1 including means supporting the seating member to confine the application of force from the seating member to the crystal to a force component directed along a fixed line passing through the contact region. 
     
     
       6. A force transducer comprising: a plate-shaped crystal having a peripheral edge with a curved portion,   at least one seating member which engages the curved portion of the peripheral edge of the crystal and has a convex surface curved in the direction opposite to that of the peripheral edge curved portion providing a contact region which is limited in length along the length of the peripheral edge, and   means for moving the surface of the seating member which engages the peripheral edge of the crystal in a direction tangential to the peripheral edge of the crystal at the contact region to adjust the position of the contact region between the seating member and the peripheral edge of the crystal.   
     
     
       7. A force transducer according to claim 6 wherein the seating member has a cylindrical shape and is supported for rotation about its axis in the support means. 
     
     
       8. A force transducer according to claim 1 wherein the curved portion of the peripheral edge of the crystal has a radius smaller than that of the adjacent portions of the peripheral edge. 
     
     
       9. A force transducer according to claim 8 wherein the crystal has a rectangular shape with the curved portion of the peripheral edge located at a corner of the crystal.